Another reason to avoid commercial pectin is the amount of sugar that is required for it to work properly.
Pectin is very concentrated in cores and skins of green crab apples. I pick the best looking ones and soak in a cold water bath with some apple cider vinegar to get them all squeaky clean. Add about a 1/4 cup to every gallon of water .
5 lb Apples
6 cups Water
juice from 1 lemon
muslin cloth and a colander